Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $57.97   13.661%   $65.8893   $65.89   $65.90   $65.90  
  Purchase #2 $123.61   5.401%   $130.2862   $130.29   $130.30   $130.30  
  Purchase #3 $191.71   5.146%   $201.5754   $201.58   $201.60   $201.60  
  Purchase #4 $61.66   12.106%   $69.1246   $69.12   $69.10   $69.10  
  Purchase #5 $149.34   12.835%   $168.5078   $168.51   $168.50   $168.50  
  Purchase #6 $219.81   6.644%   $234.4142   $234.41   $234.40   $234.40  
  Purchase #7 $149.77   4.613%   $156.6789   $156.68   $156.70   $156.70  
  7 purchase totals = $953.87       $1,026.4764   $1,026.48   $1,026.50   $1,026.50